The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Broadband light sources, for example fluorescent tubes, emit polychromatic spectra. In some cases, these light sources find a use in research and commercial applications, where a plurality of spectral content is desirable and coherency is not a concern. However and especially in medical applications, it becomes more desirable to utilize monochromatic light sources, such as lasers, which target specific biochemical pathways. Early in the development of medical modalities, lasers are used due to their typically high optical power output, ease at directing a coherent beam of light towards a specific location, and their spectral specificity. However, lasers (depending on the emission wavelength) can be quite large, quite expensive, require various chemical compounds to be recharged, and require expensive optical configurations that typically require frequent calibration and maintenance. Further, due to high optical interface power, laser output tends to require optical attenuation to bring the light levels to a safe and non-destructive level for medical applications. Finally, due to their size and complexity, it may be unwieldy and impractical to combine several lasers into a single optical interface, when such a singular output containing multiple specific monochromatic wavelength peaks is desirable.
Lasers for use in medicine are eventually replaced by newer light source technologies as they become available. Light Emitting Diodes (LEDs) represent one such technology that has found widespread use in commercial application. LEDs are monochromatic with only slightly more spectral content, low power, low cost relative to lasers, require no maintenance, have long useful emission life, and are quite small and can be mounted directly to circuitry which drives them. LEDs do represent some obstacles depending on the application, including “droop” or the reduction in optical interface power over the life of the device (typically to about 50% of initial optical interface power), non-coherent light output requiring some lensing, and in some instances much lower optical interface power. As well, with both lasers and LEDs, thermal management is critical to ensure proper wavelength stability, optical interface power, and longevity of the devices.
In the case where a designer wishes to combine multiple monochromatic wavelengths into a single optical interface for therapeutic medical applications, the designer desires to achieve an additive or synergistic effect. In terms of pharmaceutical studies, researchers may examine the concomitant use of pharmaceuticals to achieve additional benefit for the patient. For example, when two pharmaceuticals are administered to a patient, they may partially or wholly cancel the effects of each other (“destructive”); they may neither negate nor improve upon the effects of each other (“non-additive”); they may combine in such a way as to be essentially merely additive, or they may combine in such a way as to work together to achieve higher levels of clinical efficacy than would be expected from merely additive activity (i.e. provide a synergistic effect).
In the case where a designer wishes to combine multiple monochromatic wavelengths into a single optical interface for therapeutic medical applications, it is common in the art to develop an optical “combiner”. Off the shelf combiners are typically only available for lasers, generally utilizing a partially hollow cube shaped housing having two openings for laser input (often at right angles to one another). A wavelength selective dichroic mirror is oriented at 45 degrees relative to the laser inputs. Such dichroic mirror has an optical coating that allows one wavelength to pass through it, the “primary laser wavelength”, while a second wavelength, the “secondary laser wavelength”, is reflected in the direction of the primary laser wavelength's passing beam. The combined laser beam then strikes the face of an optical conduit, for example an optical fiber, whereby the combined laser beam may be directed as the designer sees fit. Optical combiners are typically only available for two lasers. The general principle allows for expansion using additional dichroic mirrors in a similar fashion as described above, however these typically are designed specifically for each application. The use of coherent laser light permits accurate aiming of each laser beam such that a maximum light transmission from laser output to optical fiber face is achieved, and the coherent nature of the light allows the face of the fiber optic to accept a great deal of light as the acceptance angle of the fiber optic is far wider than the divergence of the incoming laser beam over the distances used. Commercially, this setup requires a large amount of space, a high degree of skill on the part of the builder/assembler of the device, and (for reasons described above) may not be commercially viable. This is particularly true for devices where more than two wavelengths are to be combined into a single optical interface. For this reason this type of device is typically utilized only for research purposes. It is noteworthy that, while laser diodes have become exceedingly small for some wavelengths, many known therapeutic wavelengths outputs are available only from large format laser sources, with many of the aforementioned difficulties.
Due to the non-coherent nature of LEDs, combining multiple LED wavelengths using an optical combiner can be exceedingly challenging. Typical LEDs present with a field of view, an emission pattern, that is 120 degrees wide or more. When directing this light into a typical optical fiber which can accept light at an angle of 25.4 degrees or less, a great deal of light from the LED will be lost if the light from the LED isn't first collimated (light effectively bent by lensing such that the majority of light is parallel to a central axis of the LED die) and/or reduced. The concept of the emission pattern of LEDs covering a wide angular range is referred to as “angular content”. It is commonly held in the art that a good transmission percentage, from the light output by the LED, to that which is successfully coupled to an optical fiber be 1%, which puts a great demand on the designer to produce as much light as possible from the LED. There are many additional considerations and challenges to the design of an LED-based optical combiner, especially one that requires more than two LED inputs, will be described further in the document. However, the low cost of LEDs, the long life of LEDs, the small size of LEDs, and the most recent advancements in LED technology warrant the examination of an LED optical combiner as a commercially viable technology.
Thus, there is still a need for a compact, efficient, and readily manufacturable device for combining light from multiple non-coherent light sources.